package threading;

import java.util.Scanner;

public class lianxi2 {
    public static void main(String[] args) throws InterruptedException {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        int count = 0;
        int[][] array = new int[a][b];
        for(int i=0;i<a;i++){
            for(int j=0;j<b;j++){
                if(array[i][j]==0){
                    count++;
                    if(i+2<a){
                        array[i+2][j]=1;
                    }
                    if(j+2<b){
                        array[i][j+2]=1;
                    }
                }
            }
        }
        System.out.println(count);
    }
}